The present invention relates to a method for fabricating a fine pattern that has a periodic array structure and utilizes a self-organizational phase separation structure of a block copolymer.
The method for pattern formation according to the present invention is suitable for use, for example, in the manufacture of high-density recording media and highly integrated electronic components.
A recent rapid improvement in function of information technology equipment such as personal computers relies greatly on advance in microfabrication technology used, for example, in the manufacture of semiconductor devices. Up to now, an attempt to increase the fineness of fabrication dimension has been forwarded mainly by using an exposure light source, which emits shorter wavelength light, in lithography. Increased fineness of fabrication dimension and increased pattern density, however, have led to huge cost of lithography in the manufacturing process. Improving the fineness of pattern dimension to smaller than 100 nm is required of next generation semiconductor devices or high-density microfabricated recording media, such as patterned media. For example, electron beams are considered effective as an exposure light source for this purpose. This, however, involves a large problem with fabrication throughput.
Under the above circumstances, fabrication methods utilizing a phenomenon that a material forms a specific ordered array pattern in a self-organizational manner, have been proposed as a fabrication method that is low in cost and, at the same time, can realize high throughput. Among others, according to a method utilizing a “block copolymer,” a single-layer ordered array pattern can be formed by a simple process in which a solution of a block copolymer dissolved in a suitable solvent is coated onto an object, and the application of this method as a microfabrication method has also been reported (see, for example, R Mansky et al.; Appl. Phys. Lett., vol. 68, p. 2586 and M. Park et al.; Science, vol. 276, p. 1401).
These proposed methods comprise removing one polymer phase having a phase-separated structure of a block copolymer by ozone treatment, plasma etching, electron beam irradiation or the like to form a concave-convex pattern and fabricating an underlying substrate using the concave-convex pattern as a mask.
In general, however, the size in the layer thicknesswise direction of the phase-separated structure of the block copolymer is equal to or smaller than the size of a pattern formed in a two-dimensional direction on the substrate, and, hence, it is difficult to satisfactorily ensure etching resistance of the pattern formed as the mask. Accordingly, when the object is etched using this phase-separated structure of the block copolymer mask as an etching mask, the fabrication of a structure having a satisfactorily high aspect ratio is impossible.
In order to solve the above problem, a method has also been proposed which comprises once transferring a self-organized pattern of a block copolymer onto a pattern transfer film underlying the block copolymer, for example, by plasma etching, and etching an underlying thick resist film by oxygen plasma using the pattern transfer film as an etching mask to transfer a high-aspect ratio pattern onto the underlying resist film (see JP-A 2001-323736 (Kokai) and M. Park et al.; Appl. Phys. Lett., vol. 79, p. 257).
Also in this method, however, since a high aspect ratio is not obtained in the transfer of the block copolymer onto the pattern transfer film, in some cases, the pattern cannot be faithfully transferred without difficulties. Unsatisfactory aspect ratio in etching means that very small unevenness of film thickness distribution and self-organized pattern in the block copolymer film is highlighted as a variation in etching depth in the pattern transfer film and is transferred onto the pattern transfer film. In the extreme case, this can result in disappearance of a part of a pattern in the underlying resist film.
A method for amplifying etching selection ratio of a diblock copolymer comprising components different from each other in etching aspect ratio has been proposed as a method for overcoming the above drawback (see JP-A 2003-155365). This method comprises bringing one component in the diblock copolymer to a concave form by plasma etching, filling the concaves with a component having high etching resistance such as a silicon compound by spin coating, and again transferring the pattern onto the underlying film by plasma etching. This method suffers from a problem of complicated process.
On the other hand, in the utilization of the self-organization, the regulation of the ordered array direction of the ordering is also important. In the case of patterned media expected to realize high density in magnetic recording media, access to each of patterned magnetic material particles is required in reproduction or recording. In this case, in order that a reproduction head tracks a record line, the magnetic material particles should be arranged in one direction.
Electronic elements such as quantum effect devices, which handle single electrons and the like as information, are expected as elements that have the potential to realize a further improvement in density and power consumption over the current semiconductor devices. Also in this case, an electrode for detecting signals should be disposed in the structure that develops quantum effect. Accordingly, the microstructure which develops quantum effect should have a predetermined array, and, at the same time, the formed region should be properly regulated.
In order to regulate the array direction of the self-organization of the block copolymer, a proposal has been made in which a groove structure is previously formed in a substrate and the array direction of the particles is regulated using the groove structure as a guide (see R. A. Segalman et al.; Bulletin of the American Physical Society, Vol. 45, No. 1, p. 559, ibid., Vol. 46, No. 1, p. 1000, M. Trawick et al.; and ibid., Vol. 46, No. 1, p. 1000). In the above methods, the array direction of the diblock copolymer can be rendered uniform, but on the other hand, as described above, since the aspect ratio in the phase separated structure of the diblock copolymer is low, the formation of a pattern having a satisfactorily high aspect ratio by etching is impossible. Further, at the present time, any method for depositing the diblock copolymer only in any desired region has not been proposed.
Studies on techniques for forming a fine pattern utilizing the self-organization of a specific block copolymer have also been made (see Erik M. Freer et al.; Nano Letters, 2005, Vol. 5, No. 10, p. 2014 to 2018). Methods proposed in these studies, however, also have many problems with compatibility and cannot be said to be effective for stably forming high-quality fine patterns.